1. Field of the Invention
The invention relates to the field of cardiology. More specifically, the invention relates to a method for diagnosing and treating the heart by facilitating access to the pericardial space.
2. Background Art
An important problem in cardiology is the provision of a safe method for diagnosing and treating the heart selectively and without thoracotomy (open chest surgery). Diagnosis or treatment may be pharmacologic or electrophysiologic. For example, in order to deliver electrical stimuli directly to the heart for the purpose of cardioversion or defibrillation, patients often undergo a thoracotomy under general anesthesia for attachment of a "patch" electrode to the epicardial surface. This procedure requires an extensive incision of the pericardium. The "patch" electrode provides a large electrode surface area in contact with the heart so that a sufficient mass of cardiac tissue may be depolarized. Thoracotomy creates the additional complication of wound healing.
It is desirable to provide a method for placing the defibrillation/cardioversion electrodes in contact with the heart muscle without thoracotomy. U.S. Pat. Nos. 4,181,562 and 4,319,562 to Crosby, and 5,033,477 to Chin et al. disclose methods for placing electrodes in contact with the heart muscles from within the pericardial space without the need for thoracotomy. Access to the pericardial space is gained via a sub-xiphoid route.
This involves penetrating the chest wall below the xiphoid process.
The sub-xiphoid route has several disadvantages. First, because the pericardial sac which surrounds the heart is a tight-fitting fibrous membrane, the pericardial space is so small that it is difficult to penetrate the sac without also puncturing, and thereby, damaging the heart itself. Second, accessing the heart via the sub-xiphoid route entails a high risk of infection. These are likely to account for its failure to be adopted into common clinical practice.
In fact, the sub-xiphoid route is presently used almost solely for pericardiocentesis, a process for the aspiration of excess fluid from the pericardial sac. Pericardiocentesis is normally performed to treat cardiac tamponade, a build-up of excess fluid in the pericardial sac. The excess fluid distends the pericardial sac away from the heart such that the risk of puncturing the heart is reduced, but the risk of infection remains high.
U.S. Pat. Nos. 4,884,567 to Elliott et al., 4,946,457 to Elliott, and 4,998,975 to Cohen et al. disclose methods for transvenous implantation of electrodes into the pericardial space. A catheter is introduced through a vein to the atrium where the lateral atrial wall is penetrated in order to introduce electrodes into the pericardial space. A major problem encountered by these methods is how to penetrate the lateral atrial wall without also puncturing the tight-fitting pericardium.
The methods of these patents attempt to solve this problem through several elaborate schemes. One scheme involves using complex catheters to attach to the lateral atrial wall and to pull it back away from the pericardium prior to penetrating the wall in order to avoid puncturing the pericardium. Another approach involves injecting a fluid into the pericardial space to distend the pericardium away from the lateral atrial wall prior to penetrating the wall.
U.S. Pat. No. 4,991,578 to Cohen discloses a method for implanting epicardial defibrillation electrodes into the pericardial space. The method involves entering the pericardial space via the sub-xiphoid route. As discussed above, it is difficult to penetrate the pericardial sac via the sub-xiphoid route without also puncturing, and thereby damaging, the heart itself. Like the method discussed directly above, the '578 patent discloses injecting a fluid into the pericardial space or attaching and pulling on a catheter to distend the pericardial sac away from the heart.
Because each of these known methods is intrinsically cumbersome and hazardous, they have not gained widespread use. What is needed is a simpler, safer, and more effective way of accessing the pericardial space for delivery of electricity directly to the heart muscle.
In addition to providing a convenient location for placement of electrodes, the confines of the pericardial sac provide an excellent opportunity to isolate the heart for treatment and diagnosis. By introducing pharmacologic agents directly into the pericardial sac, high cardiac drug concentrations can be achieved without spillage or systemic distribution to other organs or tissues.
The pericardial sac has been used for containment of pharmacologic agents for a number of years in experimental settings, but delivery has heretofore required open chest surgery to access the pericardial space. U.S. Pat. Nos. 4,003,379 and 4,146,029 to Ellinwood disclose an implantable medication dispensing apparatus which is adapted to dispense drugs to the pericardial sac over a long period of time, for example, to prevent arrhythmias. The Ellinwood patents, however, do not teach a method for routing the drugs into the pericardial sac.
U.S. Pat. No. 5,269,326 to Richard L. Verrier discloses a method for transvenously accessing the pericardial space via the right auricle. The full text of the Verrier '326 patent is incorporated herein by reference as if reproduced in full below. The transvenous method described by Verrier overcomes the limitations noted above with prior methods by providing a method for safely and reliably introducing a catheter and/or electrodes into the pericardial space. The present invention improves upon the Verrier '326 patent by providing a specific method for exploiting the route discovered by Verrier.